Method for directly cooling fine-particle solid substances

ABSTRACT

The invention relates to a method for directly cooling fine-particle, powdery solid substances by using a cooling medium provided in the form of low-boiling condensed gases or of cold gases obtained therefrom, whereupon bulk material packings are subsequently filled with these solid substances. The invention also relates to a device for directly cooling the fine-particle, powdery solid substances and to fine-particle, powdery solid substances, which are located inside bulk material packings and which, compared to air, have a lower oxygen content in the gas phase between the solid substance particles.

[0001] The invention relates to a method and a device for directlycooling fine-particle, powder-form solid substances before they arefilled into bulk material packaging, according to the preambles ofclaims 1 and 23.

[0002] Numerous fine-particle, powder-form solid substances are filledinto bulk material packaging for the purpose of sale, transport,protection against ambient influences, or for the purpose of storage.Frequently, the temperature of the fine-particle, powder-form solidsubstances is too high, as a result of the production processes orprocessing processes, for them to be filled into the desired bulkmaterial packaging without problems. Without sufficient cooling, thiscan therefore result in numerous problems or disadvantages, such as:

[0003] severe wear of temperature-sensitive system parts such as rubbergaskets or pinch valves,

[0004] damage to bulk material packaging, such as paper or plastic bags,due to an overly high temperature of the solid substances,

[0005] low bulk weight of the solid substances at the time of packaging,

[0006] poor de-aeration behavior during filling of the bulk materialpackaging and silo vehicles due to the comparatively high viscosity ofthe hot gas phase,

[0007] low fill amount of bulk material packaging and silo vehicles,

[0008] more time-consuming filling of bulk material packaging and silovehicles,

[0009] damage to bulk material packaging (e.g. paper bags) due to anoverly high fill volume,

[0010] great tendency to produce dust while filling the solid substancesinto bulk material packaging,

[0011] optically unappealing appearance of bags and pallets,

[0012] condensation effects within pallets that are shrink-wrapped,

[0013] impairment of work safety during further handling (e.g. loadingor transport) due to the hot surface of the bulk material packaging.

[0014] In this connection, the stated problems or disadvantages duringfilling of fine-particle, powder-form solid substances into bulkmaterial packaging can occur both individually and in combination. Someof the stated problems or disadvantages are obvious, if hot solidsubstances must be handled and filled into bulk material packaging,others of the stated problems or disadvantages (such as low bulk weight,poor de-aeration behavior) are, however, specific for the handling andfilling of very fine-particle, powder-form solid substances into bulkmaterial packaging. In this sense, such powder-form solid substances arereferred to as fine-particle in the present document if they have anaverage particle size of less than 50 μm, preferably less than 20 μm,but particularly if they have an average particle size of less than 5μm, preferably less than 1 μm.

[0015] Bulk material packaging in the present document is understood tomean such packaging that is used for the purpose of sale, transport,protection against ambient influences, or for the purpose of long-termstorage, for example paper or plastic bags, barrels, Big Bags, sacks,containers made of paper, paperboard, plastic, or other materials.

[0016] Fundamentally, such problems can occur when filling allfine-particle, powder-form solid substances into bulk materialpackaging, if they have a higher temperature due to the method of theirproduction or processing, e.g. after calcinations, calcinations withsubsequent grinding, drying, or any other high-temperature treatment, orin the case of a production method at a high temperature. For example,this applies to cement, carbon black, or also to pigments pretreated inthermal manner, e.g. by means of calcinations, which must be filled intobulk material packaging. In particular manner, however, this applies topigments ground by steam jet.

[0017] For the grinding of very fine-particle solid substances havingparticle sizes in the range of 1 μm or below, the technique of jetgrinding is frequently used. Jet grinding is a kind of impact grindingin which the material being ground is accelerated in a fast gas streamand comminuted by means of rebounding against itself or against arebound wall. In this connection, the grinding effect is decisivelydependent on the impact velocity, i.e. the impact energy.

[0018] In the grinding of solid substances that require a particularlyhigh introduction of energy or a particularly high degree of comminutionin order to be comminuted or de-agglomerated, such as in the case ofvarious inorganic pigments, the method of steam jet grinding usingsuperheated steam as the grinding medium is generally used. A method forthe production of titanium dioxide pigments, in which the titaniumdioxide is subjected to steam jet grinding in a final step, is describedin DE 195 36 657 A1. During steam jet grinding, the temperature of thepigment/gas mixture generally lies in the range of approximately 200 to300° C. after it leaves the mill. After separation of the pigment fromthe steam by means of a dust precipitator or dust filter, thetemperature of the bulk pigment, which still contains steam, typicallystill lies in the range of approximately 200 to 250° C. It is true thata certain cooling occurs as the result of intermediate storage in silosor during mechanical or pneumatic transport, but at the time of beingfilled into bags or other packaging, the pigments are frequently stillat temperatures of about 100° C. or more. This can result in numerousproblems or disadvantages, as already described above.

[0019] The cooling effect of fine-particle, powder-form solid substancesby means of the addition of air at ambient temperature, e.g. duringpneumatic transport of the fine-particle, powder-form solid substances,is limited because of the slight temperature difference and the low heatcapacity of the air. This has the result that even when using largeamounts of air, the temperature reduction is comparatively slight andaccordingly, the disadvantages described above are only ameliorated toan insignificant extent. It is true that a very large amount of air cancause a significant temperature reduction, but this method of procedurehas significant disadvantages with regard to separation of the gas phasefrom the fine-particle, powder-form solid substances, as well as withregard to packaging properties and operating costs. Furthermore, therisk of contamination of the fine-particle, powder-form solid substanceswith moisture, dust, carbon dioxide, sulfur oxides or nitrogen oxides,traces of oil, or other contaminants from the air increases.

[0020] Convection cooling over an extended period of time is alsodisadvantageous because of the poor heat conductivity of mostfine-particle, powder-form solid substances and accordingly, anunreasonably long period of occupation of bulk material containers. Thiscan result in a significant reduction of production capacity.

[0021] DE 3 414 035 A1 describes the indirect cooling of a gas thatcontains dust, in which the gas is passed over regenerators filled witha heat storage mass. This or comparable methods for indirect cooling bymeans of cooling surfaces or heat exchangers is/are not very practical,since sizable heat transfer surfaces would have to be made available forthis purpose. In the case of this method described in DE 3 414 035 A1,the dust load of the gases is furthermore very slight, at approximately20 mg/m³, and is not comparable with the usual solid substance/gasmixture ratios that are usual in pigment technology, for example, duringthe intended filling into bulk material packaging (frequently severalkg/m³). Experience has shown that with higher solid substance contentsin the gas phase, the risk of caking to the cooling contact surfacesincreases. Cooling coils for indirectly cooling fine-particle,powder-form solid substances are used in various cases, but here again,the disadvantages in terms of caking, operational safety, and investmentcosts are significant.

[0022] DE 3713571 A1 describes a device for filling plastic bags withpowder-form or granulated materials, wherein the filled bags are sealedand brought into a cooling zone, in order to guarantee the stability ofthe seal seam. Since the cooling described here only takes place afterfilling into bags, it is not suitable for avoiding the disadvantagesstated above.

[0023] U.S. Pat. No. 3,664,385 describes mechanical compacting ofpowders for filling them into packaging, wherein a pulse of cooled aircan also be used for eliminating dust. However, the cooling effect ofsuch a pulse of cooled air is insufficient for achieving adequatecompacting of fine-particle, powder-form solid substances, and for thisreason, the powders also have to be compacted mechanically. Furthermore,this method is less suitable for fine-particle, powder-form solidsubstances having particular requirements with regard to dispersabilityand fineness, such as pigments, since the mechanical compacting bringswith it the risk of agglomeration, and thereby the purpose aimed at withgrinding can be partially eliminated again.

[0024] U.S. Pat. No. 4,619,113 describes direct cooling of detergentpowder in a silo, using liquid nitrogen, in order to subsequently allowthe addition of temperature-sensitive detergent powder additives. Sincethe average particle size of the detergent powder to be cooled is 500 μm(column 1, lines 24-25), this method described in U.S. Pat. No.4,619,113 does not provide any indication of the particular problemswhile filling very fine-particle, powder-form solid substances into bulkmaterial packaging, nor of how to solve them.

[0025] DE 3941262 describes direct cooling of a powder-form substance,using liquid nitrogen, wherein the powder jet is scattered by means ofmechanical installations before it makes contact with the liquidnitrogen. DE 3623724 A1 l describes direct cooling of cement, usingliquid nitrogen, wherein the cement is blown into the silo at the sametime as the liquid nitrogen. These methods described in DE 3941262 andDE 3623724 A1 have the sole purpose of simple cooling, not that ofimproving the filling properties for packaging in bulk materialpackaging. These references do not give any indication with regard tothe specific requirements of very fine-particle, powder-form solidsubstances, nor do they give any indications with regard to the specificproblems stated above and how to solve them, during the handling andfilling of fine-particle, powder-form solid substances into bulkmaterial packaging.

[0026] U.S. Pat. No. 3,350,046 describes the heat exchange between gasesand fine-particle solid substances having a particle size of less than50 μm, wherein a device consisting of several chambers, connected withone another, is used, through which the gas and solid substance streamtakes place in opposite directions. The system used for this purpose iscomplicated, and a large amount of cooling gas is needed. The methodtherefore has similar disadvantages as the cooling with large amounts ofair that was described above. There are also no indications of thespecific problems stated above and how to solve them, during thehandling and filling of fine-particle, powder-form solid substances intobulk material packaging.

[0027] EP 611 928 A1, EP 501 495 A1, and DE 38 33 830 A1 describe directcooling of material to be ground, using condensed gases having a lowboiling point. This cooling takes place, however, before grinding, inorder to optimize the actual grinding process by increasing thebrittleness of the material to be ground, and accordingly does not leadto a solution of the problems described above.

[0028] The temperature reduction before grinding that is achieved bysuch cooling is generally lost again as a result of the heat developmentthat is connected with grinding, so that no advantages exist any longerat the time of filling. There are also no indications of the specificproblems stated above and how to solve them, during the handling andfilling of fine-particle, powder-form solid substances into bulkmaterial packaging.

[0029] Most of the methods mentioned are aimed at reducing obviousthermal consequential problems by means of various variants of cooling.However, there are no explicit indications of the specific requirementsof fine-particle, powder-form solid substances, e.g. the very highrequirements with regard to fineness and dispersability of pigments, andthe related problems during filling into bulk material packaging. It istherefore a disadvantage of the stated methods that they do noteliminate the problems described in the handling and filling offine-particle, powder-form solid substances into bulk materialpackaging, or eliminate them only in part. This is particularly true forthe pigment-specific problems that were described.

[0030] An aim was to make available a method that makes it possible totreat a hot, fine-particle, powder-form solid substance in such a mannerthat the disadvantages described above, in the handling offine-particle, powder-form solid substances and their subsequent fillinginto bulk material packaging, are avoided entirely, or at least to agreat extent. It was furthermore an aim to use as low a gas volume aspossible in the handling of the fine-particle, powder-form solidsubstances and their filling into bulk material packaging, in order tokeep the expense and effort of separation of the gas and the removal ofdust from it as low as possible.

[0031] In addition, it was an aim to make available a device with whichcooling of a mixture consisting of a fine-particle, powder-form solidsubstance and a gas can be accomplished in simple and efficient manner.In addition, it was an aim to produce fine-particle, powder-form solidsubstances located in bulk material packaging that have a lowerproportion of oxygen in the gas phase between the solid substanceparticles, as compared with air.

[0032] This aim is achieved by means of a method and a device accordingto claims 1 and 23.

[0033] The method according to the invention comprises directly coolingfine-particle, powder-form solids by adding a cooling medium and,subsequent to this, filling the ground material into bulk materialpackaging, wherein the cooling medium consists either of one or moredifferent condensed gases having a low boiling point, or of a cold gasor gas mixture, which was produced using one or more different condensedgases having a low boiling point, or wherein the cooling medium consistsof a cold gas or gas mixture that was pre-cooled using one or moredifferent condensed gases having a low boiling point. This method is ofparticular significance for cooling and subsequent filling offine-particle, powder-form solid substances into bulk materialpackaging, such as commercially available paper bags, plastic bags,sacks, barrels, or other small containers made of different materials.The method can also be advantageous for the filling of silo vehicles.

[0034] Any compounds that demonstrate an inert behavior with regard tothe fine-particle, powder-form solid substances in question are suitableas a cooling medium. These can be, for example, noble gases, carbondioxide, nitrogen, oxygen, or mixtures of the stated substances (e.g.air). Preferably, the cooling medium used for direct cooling is obtainedby means of evaporation of condensed gases having a low boiling point.Liquid nitrogen, liquid air, or liquid carbon dioxide are particularlysuitable. Solid carbon dioxide is also suitable, particularly if it ispresent in finely dispersed form. In this connection, the cooling mediumused for direct cooling preferably has a temperature of less than 0° C.,preferably less than −20° C., particularly preferably less than −40° C.,in order to achieve a significant cooling effect.

[0035] The temperature aimed at for the fine-particle, powder-form solidsubstances to be cooled, i.e. the solid-substance-containing mixture tobe cooled is, of course, dependent on the type of solid substances andthe quality demands made on it. Preferably, the type and amount of thecooling medium is selected in such a way that the fine-particle,powder-form solid substances to be cooled are cooled by at least 20° C.,preferably by at least 50° C. Cooling by means of the direct cooling toa maximum of 100° C., and in particular to a maximum of 70° C., ispreferred.

[0036] Preferably, the cooling medium used for direct cooling containsless than 0.0001 parts by mass water. In this way, the dew point of thesolid substance/gas mixture can be lowered, thereby resulting in areduced tendency of the solid substances to form agglomerates. Forexample, the dew point in the solid substance bulk material can beadvantageously lowered by using liquid nitrogen with its extremely lowcontent of water.

[0037] Cooling of the fine-particle, powder-form solid substances canfundamentally take place at different points of the production processor processing process, for example directly after thermal treatment ofthe powder-form solid substances, in transport lines, or directly beforefilling into bulk material packaging.

[0038] The method according to the invention is particularly practicalif the fine-particle, powder-form solid substances are produced orprocessed at high temperatures because of conditions of processtechnology or logistical requirements, and the temperature can belowered by means of convection cooling or cooling with air only to aninsufficient degree, so that conventional filling into bulk materialpackaging brings significant problems with it.

[0039] Examples of processes in which the cooling according to theinvention can have an advantageous effect:

[0040] direct cooling and packaging of fine-particle, powder-form solidsubstances subsequent to thermal drying and, if applicable, grinding,

[0041] direct cooling and packaging of fine-particle, powder-form solidsubstances subsequent to calcination and, if applicable, grinding,

[0042] direct cooling and packaging of fine-particle, powder-form solidsubstances subsequent to a pyrrolytic production process or a combustionprocess,

[0043] direct cooling and packaging of fine-particle, powder-form solidsubstances subsequent to steam jet grinding.

[0044] It has been shown that in the case of fine-particle, powder-formsolid substances having an average particle size of <50 μm, preferably<20 μm, but particularly in the case of very fine-particle, powder-formsolid substances having an average particle size of <5 μm, particularlypreferably <1 μm, the rheological properties, i.e. the handlingproperties are clearly dependent on their temperature. Thus, forexample, the bulk weight of fine-particle, powder-form solid substancesthat are filled into the packaging usually used, such as bags, barrels,Big Bags, or silos, at a low temperature, is significantly greater incomparison with the same product that is filled into this packaging at ahigher temperature.

[0045] The fine-particle, powder-form solid substances to be cooled andpackaged can be, for example, titanium dioxide, iron oxide, chromiumoxide, photo-resistant pigments, colored pigments, metal pigments,magnetic pigments, carbon blacks, or cement. Also, the fine-particle,powder-form solid substances to be packaged can be temperature-sensitivecompounds or solid substances coated with temperature-sensitivecompounds.

[0046] The direct cooling according to the invention, using a coolingmedium, can take place, for example, in that the cooling medium ismetered into a transport line for pneumatic transport of thefine-particle, powder-form solid substances. It can be advantageous tometer the cooling medium in at several different locations, in order toachieve particularly great temperature reductions. In this manner, thecooling medium can also make a significant contribution to the pneumatictransport, if applicable. Injection of the cooling medium into atransport line can take place both in the flow direction and counter tothe flow direction, depending on whether strong or slight swirling ofthe cooling medium is aimed at. The device for direct cooling accordingto the invention consists of a supply container for condensed gas havinga low boiling point, an insulated connecting line between the supplycontainer and the transport line for pneumatic transport of thefine-particle, powder-form solid substances, a nozzle for introductionof the condensed gases having a low boiling point into the transportline, and a control and regulation device.

[0047] This method of direct cooling according to the invention has theadvantages, as compared with the method of indirect cooling by way ofcontact surfaces, that no large contact surfaces for heat transfer arerequired. In addition, cooling takes place significantly more rapidlythan in the case of indirect cooling, which is particularly advantageousif the ground material in question is temperature-sensitive, or if greattemperature reductions are aimed at within a short period of time.

[0048] In contrast, in the case of indirect cooling, there is the riskof local condensation because of the comparatively great temperaturegradients in the material to be cooled, particularly in the region ofthe cooling surfaces.

[0049] The advantage of the method according to the invention ascompared with cooling using large amounts of air at the ambienttemperature is, for one thing, that a significantly more rapid andstronger cooling effect can be achieved by means of direct cooling usingcondensed gases having a low boiling point, because of their evaporationenthalpy. For another thing, a lesser volume of gas phase is required inthe method according to the invention, which significantly simplifiesthe separation of the gas phase from the fine-particle, powder-formsolid substances before or during filling into bulk material packaging.In addition, the expense and effort for removing dust from the gases issignificantly reduced. Aside from this, contamination of thefine-particle, powder-form solid substances with moisture, dust, carbondioxide, sulfur oxides or nitrogen oxides, traces of oil, or othercontaminants from the air is reduced or avoided; particularly in thecase of a basic surface of the fine-particle, powder-form solidsubstances (e.g. after chemical treatment with corresponding compounds),undesirable neutralization of the surface by the acid components in theair can occur when using large amounts of air. Finally, the residualmoisture of the fine-particle, powder-form solid substances is reducedby means of the cooling medium, which is generally very dry and has ahigh absorption capacity for moisture.

[0050] Although the cryogenic cooling of fine-particle, powder-formsolid substances by means of condensed gases having a low boiling pointis characterized by relatively high costs for the cooling medium, thiseffect is surprisingly overcompensated by a whole number of advantagesof this method of procedure, at a closer look. For example, because ofthe lower temperature of the solid substance/gas mixture, and because ofthe lower specific gas proportion (with reference to the solidsubstance), the following advantages can result:

[0051] less wear of temperature-sensitive system parts such as rubbergaskets,

[0052] less damage to temperature-sensitive bulk material packaging,such as paper or plastic bags, due to a lower temperature of thefine-particle, powder-form solid substances to be packaged,

[0053] because of less thermal stress, the possibility of using lessexpensive packaging,

[0054] greater bulk weight of the fine-particle, powder-form solidsubstances at the time of packaging,

[0055] better de-aeration behavior during filling of the bulk materialpackaging and silo vehicles due to the lower viscosity of the gas phase,

[0056] higher fill amount of bulk material packaging and silo vehicles,

[0057] faster filling of bulk material packaging and silo vehicles,

[0058] less damage to bulk material packaging (e.g. paper bags) due toan overly high fill volume,

[0059] less tendency to produce dust while filling the fine-particle,powder-form solid substances into bulk material packaging,

[0060] less gas volume during pneumatic transport or cooling; thereforesmaller filter area for removing dust from the gas, i.e. higher fillingcapacity at a constant filter area,

[0061] optically more appealing appearance, for example of bags andpallets,

[0062] less moisture in the product due to absorption capacity of thecooling medium,

[0063] less condensation within pallets that are shrink-wrapped,

[0064] improvement of work safety, due to the lower temperature of thepackaged fine-particle, powder-form solid substances, during furtherhandling (e.g. loading or transport).

[0065] The method according to the invention for cooling fine-particle,powder-form solid substances has the result not only of a lowerproportion of defective batches, such as burst bags, but also hasreliable operation, an increased capacity of packaging devices, as wellas a reduced tendency to produce dust, as additional advantages, andresults in a more appealing optical appearance of individual bags orpallets.

[0066] The method according to the invention is particularly suitablefor directly cooling inorganic or organic pigments and their subsequentfilling into bulk material packaging, because particularly great demandswith regard to dispersability or fineness are often made with regard tothese pigments and, at the same time, the rheological properties, i.e.the handling of the ground pigments, are of particular importance. Thespecific advantages of the method according to the invention, in thecase of use for pigments, are that significant demands with regard tothe pigments, such as good dispersability, good optical properties, andgood handling of the ground pigments during filling into bulk materialpackaging can be fulfilled at the same time. Specifically therheological properties, i.e. the handling properties of pigments, aregreatly dependent on their temperature. Thus, for example, the bulkweight of pigments that are filled into the packaging normally used,such as bags, barrels, Big Bags, or silos, is significantly greater incomparison with the same product that was filled into this packaging ata higher temperature.

[0067] In the case of steam jet grinding of pigments, cooling of theground material can [take place] directly behind the steam jet mill,after a separation device such as a dust filter or a dust precipitatorin the transport line, or directly before filling into bulk materialpackaging. It can be advantageous if the cooling medium is only addedwhen the partial steam pressure of the gas phase of the ground materialalready has sufficiently low values, for example due to partial exchangeor dilution of the steam by air, in order to avoid going below the dewpoint as a result of the direct cooling. It is preferred if after steamjet grinding, part of the gas phase that contains steam is first removedfrom the ground pigments, and subsequently the ground pigments arecooled by means of direct cooling, using a cooling medium. This removalof part of the gas phase that contains steam takes place, for example,using a dust precipitator and/or a dust filter.

[0068] The method according to the invention is particularly well suitedfor titanium oxide pigments, because of the strong influence of thetemperature on parameters such as the bulk weight during packaging. Themethod according to the invention proves to be particularly advantageousfor those titanium oxide grades that are used for coloring plastics orfor dispersion paints, and have a particularly low bulk weight becauseof their specific composition. In this manner, alternative methods suchas granulation or pelleting can be eliminated. Also, in the case oforganically coated pigments, a detrimental influence on the tendency oforganic additives on the pigment surface (grinding aids) to decomposecan easily result from high temperatures, and this can have aparticularly detrimental effect on the color tone. This is also avoidedby the method according to the invention. The method according to theinvention is particularly advantageous if several steam jet mills areoperated in parallel, and if the high throughput of pigment achieved inthis manner can be lowered in temperature only inadequately by means ofconvection cooling or other conventional methods.

[0069] The method according to the invention is also well suited foriron oxide pigments. The advantages here are similar to those fortitanium dioxide pigments, for one thing. In the case of iron oxidepigments that can be oxidized, e.g. iron oxide pigments in the magnetitemodification, there is the additional factor that the tendency tooxidize in the course of processing and storage can be prevented bymeans of the partial or extensive displacement of oxygen in the air bythe cooling medium, when using non-oxidizing gases such as CO₂ or N₂ asthe cooling medium. In addition, the reactivity of these pigments withregard to residual portions of oxygen in the air is clearly reduced bythe low temperatures that can be achieved by means of the methodaccording to the invention, during packaging in bags. Using the methodaccording to the invention, it is therefore possible in all cases tocomminute even those pigments that usually cannot be ground by means ofsteam jet grinding, using this decidedly effective grinding technique.

[0070] The materials obtained according to the invention and stored inbulk material packaging preferably have less than 20 wt.-% oxygen in thegas phase between the solid substance particles, particularly preferablyless than 15 wt.-% oxygen, i.e. a mass ratio of nitrogen to oxygen ofmore than 4, preferably more than 5.7.

[0071] Since fine-particle, powder-form solid substances can demonstratea clearly different rheological behavior, depending on their specificcomposition, a targeted influence on the transport properties can beundertaken by means of a suitable selection of the addition of thecooling medium and therefore of the temperature. Depending on the typeof solid substance, cooling ahead of the pneumatic or mechanicaltransport or only after transport can be more advantageous. Also,cooling that does not occur until immediately before filling into bulkmaterial packaging can be advantageous.

[0072] A preferred embodiment of the invention consists of cooling thetransport air used for pneumatic transport and undertaking directcooling of the fine-particle, powder-form solid substances using thiscold transport air as the cooling medium. In this connection, thetemperature of the transport air can take place, for example, using aheat exchanger or by means of the direct feed of condensed gases havinga low boiling point or of solid carbon dioxide into the transport air.In this connection, cooling of the transport air by means of a heatexchanger can take place according to any method known to a personskilled in the art. It is particularly advantageous in this method ofprocedure that here, indirect cooling takes place on a gas that is freeof solid substances, and that the solid substance/gas mixture is cooleddirectly.

[0073] Cooling of the transport air used for the pneumatic transport,before contact with the fine-particle, powder-form solid substance to becooled, can be more advantageous, in terms of process technology, thancooling of a gas that contains solid substances, such as that formedafter the transport air has been mixed with the fine-particle,powder-form solid substances to be transported. It is also possible tocombine the variants that have been described with one another. Forexample, both cooling of the transport air (directly or indirectly) anddirect cooling of the solid substance/gas mixture with this air can takeplace, as well as, in addition, direct cooling of the solidsubstance/gas mixture (e.g. with condensed gases having a low boilingpoint).

[0074] Independent of the type of the cooling medium, the possibility oftargeted control and regulation of the total process with regard totemperature-dependent parameters is particularly advantageous in themethod of directly cooling fine-particle, powder-form solid substances,according to the invention. For example, by regulating the amount or thetemperature of the cooling medium that is added, an optimal and constanttemperature of the fine-particle, powder-form solid substances can beadjusted as a function of the product, and thereby the transportproperties, for example, or the properties during filling of bulkmaterial packaging, can be controlled in targeted manner, optimized, andkept constant.

[0075] Filling of the fine-particle, powder-form solid substances intopaper or plastic bags usually takes place by way of a filling silo,using solid substance transport systems. At temperatures of 60° C. andhigher, the use of inexpensive plastic bags (e.g. made of polyethyleneor polypropylene) is generally eliminated. Only special and expensiveplastic bags having a high temperature stability can be used for thispurpose. Using the method according to the invention, however, it ispossible to use inexpensive polyethylene or polypropylene bags insteadof these expensive plastic bags. Generally, cooling to temperatures inthe range of 60° C. or below is required for this. The use ofinexpensive paper bags having a lesser stability, or of paper bags witha plastic lining, or plastic components in the closure region, alsobecomes possible using the method according to the invention. The methodaccording to the invention also allows the use of other packaging, whichis not resistant to the temperatures that occur according to the stateof the art, e.g. Big Bags made from plastics having a lesser thermalresistance, or other temperature-sensitive plastic packaging.

EXAMPLE 1

[0076] A titanium dioxide pigment produced according to the state of theart, subsequently treated, and dried, is micronized in a steam jet mill.The product/steam ratio is 1:2.2 parts by weight. The temperature of thesteam is 260° C. As transport air, approximately 100 m³ per metric tonof TiO₂ are introduced into the steam jet mill, together with thepigment to be ground. The temperature of the pigment/gas mixture aftersteam jet grinding is approximately 230° C.; after separation of thepigment from the gas phase, using a dust separator, the temperature ofthe bulk pigment, which still contains steam, is approximately 180° C.The water content of the gas phase is approximately 95 wt.-%, the watercontent of the gas phase with reference to TiO₂ is approximately 0.2wt.-% at a bulk density of the TiO₂ of 0.5 g/cm³. After interim storagein a silo, the bulk pigment that still contains steam is pneumaticallytransported to the bagging machine. The amount of dried transport air is75 m³ per metric ton of TiO₂. By way of a nozzle, 97 L liquid nitrogenper metric ton of TiO2 are introduced into the transport line. Thetemperature of the titanium dioxide/gas mixture is lowered from 110° C.to 60° C. in this manner. Afterwards, the water content of the gas phaseamounts to approximately 1 wt.-%, the water content of the gas phasewith reference to TiO₂ is approximately 0.2 wt.-%. Removal of the gasphase from the TiO₂ takes place in the filling silo from which the bagsare filled. The temperature of the bulk pigment that contains gas is 60°C. at the time of filling into paper bags. The composition of the gasphase between the TiO₂ particles in the paper bags is: 87 wt.-% N₂, 12wt.-% O₂. The water content of the gas phase with reference to TiO₂ iscalculated as being less than 0.01 wt.-%. Independent of this, the TiO₂has about 0.3 wt.-% adsorbed water.

[0077] The filling and de-aeration behavior during filling of the bagsis good, because of the high bulk weight of the bulk pigment thatcontains gas. As a consequence of this, the pallets demonstrate anoptically appealing appearance.

EXAMPLE 2

[0078] A titanium dioxide pigment for coloring plastics, producedaccording to the state of the art, subsequently treated, and dried, ismicronized in a steam jet mill with the addition of 1 wt.-% of a siliconoil. The remainder of the process, up to filling into bags, takes placeanalogous to Example 1. In contrast to Example 1, however, filling takesplace into commercially available polypropylene bags. Because of the lowtemperature of the bulk pigment that contains gas (60° C.) at the timeof filling into the polypropylene bags, no damage to the bags occurs.The filling and de-aeration behavior during filling of the bags is good,because of the comparatively high bulk weight of the bulk pigment thatcontains gas. As a consequence of this, the pallets demonstrate anoptically appealing appearance.

[0079] The pigment is particularly well suited for coloring plastics. Itis possible to use the pigment, together with the packaging, directly inthe processing process.

EXAMPLE 3

[0080] A titanium dioxide pigment produced according to the state of theart and subsequently treated with a total of 15 wt.-% of SiO₂ and Al₂O₃(with reference to TiO₂), and dried, is micronized in a steam jet mill.The remainder of the process takes place analogous to Example 1. Thefilling and de-aeration behavior during filling of the bags is good,because of the comparatively high bulk weight of the bulk pigment thatcontains gas. As a consequence of this, the pallets demonstrate anoptically appealing appearance. The pigment is particularly suitable forthe production of dispersion paints.

EXAMPLE 4

[0081] An iron oxide pigment (Fe₂O₃) produced according to the state ofthe art, by means of calcination, from magnetite, is micronized in asteam jet mill. The product/steam ratio is 1:2 parts by weight. Thetemperature of the steam is 260° C. The remainder of the process takesplace analogous to Example 1. The filling and de-aeration behaviorduring filling of the bags is good, because of the high bulk weight ofthe bulk pigment that contains gas. Also, it is possible to fill theproduct into conventional polyethylene or polypropylene bags, because ofthe low temperature (60° C.) of the bulk pigment that contains gas.

EXAMPLE 5

[0082] A nickel rutile yellow pigment produced according to the state ofthe art is ground in a Raymond mill. After interim storage in a silo,the bulk pigment is pneumatically transported to a bagging machine. Byway of a nozzle, an amount of liquid nitrogen is introduced into thetransport line so that the temperature of the bulk pigment that containsgas is 60° C. at the time of filling into bags. The filling andde-aeration behavior during filling of the bags is good, because of thehigh bulk weight of the bulk pigment that contains gas. Also, it ispossible to fill the product into conventional polyethylene orpolypropylene bags, because of the low temperature (60° C.) of the bulkpigment that contains gas.

EXAMPLE 6

[0083] A furnace carbon black produced according to the state of the artis separated from the gas phase by way of a dust filter, and put into asilo for interim storage. From there, the carbon black is pneumaticallytransported to a bagging machine. By way of a nozzle, an amount ofliquid nitrogen is introduced into the transport line so that thetemperature of the bulk carbon black that contains gas is 60° C. at thetime of filling into bags. The filling and de-aeration behavior duringfilling of the bags is good, because of the high bulk weight of the bulkcarbon black that contains gas. Also, it is possible to fill the productinto conventional polyethylene or polypropylene bags, because of the lowtemperature (60° C.) of the bulk carbon black that contains gas.

EXAMPLE 7

[0084] A magnetite pigment (Fe₃O₄) produced according to the state ofthe art is ground in a steam jet mill. After extensive removal of thegas phase, using a dust separator or dust filter, and interim storage ina silo, the bulk pigment is pneumatically transported to a baggingmachine, using nitrogen as the transport gas. By way of a nozzle, anamount of liquid nitrogen is introduced into the transport line so thatthe temperature of the bulk pigment that contains gas is a maximum of30° C. at the time of filling into bags. The filling and de-aerationbehavior during filling of the bags is good, because of the high bulkweight of the bulk pigment that contains gas. Also, the reactivity withregard to residual proportions of oxygen is prevented because of the lowfilling temperature. The steam-jet-ground magnetite has an excellentfineness and dispersability.

EXAMPLE 8 Comparison Example

[0085] A titanium dioxide pigment produced according to the state of theart, subsequently treated, and dried, is micronized in a steam jet mill.The product/steam ratio is 1:2.2 parts by weight. The temperature of thesteam is 260° C. As transport air, approximately 100 m³ per metric tonof TiO₂ are introduced into the steam jet mill, together with thepigment to be ground. The temperature of the pigment/gas mixture aftersteam jet grinding is approximately 230° C.; after separation of thepigment from the gas phase, using a dust separator, the temperature ofthe bulk pigment, which still contains steam, is approximately 180° C.The water content of the gas phase is approximately 95 wt.-%, the watercontent of the gas phase with reference to TiO₂ is approximately 0.2wt.-% at a bulk density of the TiO₂ of 0.5 g/cm³. After interim storagein a silo, the bulk pigment that still contains steam is pneumaticallytransported to the bagging machine. The amount of transport air is 150m³ per metric ton of TiO₂. Afterwards, the water content of the gasphase amounts to approximately 1 wt.-%, the water content of the gasphase with reference to TiO₂ is approximately 0.2 wt.-%. Removal of thegas phase from the TiO₂ takes place in the filling silo from which thebags are filled. The temperature of the bulk pigment that contains gasis 110° C. at the time of filling into paper bags. The composition ofthe gas phase between the TiO₂ particles in the paper bags is: 76 wt.-%N₂, 23 wt.-% O₂. The filling and de-aeration behavior during filling ofthe bags is poor, because of the low bulk weight of the bulk pigmentthat contains gas. As a consequence of this, the pallets demonstrate anoptically unappealing appearance. Filling into commercially availablepolyethylene or polypropylene bags is not possible, because of the hightemperature.

EXAMPLE 9 Comparison Example

[0086] A titanium dioxide pigment produced according to the state of theart, subsequently treated, and dried, is micronized in a steam jet mill.The product/steam ratio is 1:2.2 parts by weight. The temperature of thesteam is 260° C. As transport air, approximately 100 m³ per metric tonof TiO₂ are introduced into the steam jet mill, together with thepigment to be ground. The temperature of the pigment/gas mixture aftersteam jet grinding is approximately 230° C.; after separation of thepigment from the gas phase, using a dust separator, the temperature ofthe bulk pigment, which still contains steam, is approximately 180° C.After brief interim storage in a silo, the bulk pigment that stillcontains steam is pneumatically transported to the bagging machine. Inorder to achieve sufficient cooling of the titanium dioxide, 730 m³transport air per metric ton of TiO₂ are used.

[0087] Removal of the gas phase from the TiO₂ takes place in the fillingsilo from which the bags are filled. The temperature of the bulk pigmentthat contains gas is 60° C. at the time of filling into paper bags.

[0088] The removal of the gas phase is time-consuming, because of thehigh amount of gas. Only significantly less titanium oxide can betransported and packaged per time unit, if no appropriately enlargedfilter areas are made available for removing dust from the transportgas.

1. Method for directly cooling fine-particle, powder-form solidsubstances by means of adding a cooling medium, and subsequent fillinginto bulk material packaging, wherein the fine-particle solid substanceshave an average particle size of less than 50 μm, preferably less than20 μm, and whereby the cooling medium consists a) either of one or moredifferent condensed gases having a low boiling point, b) or of a coldgas or gas mixture, which was produced using one or more differentcondensed gases having a low boiling point, c) or of a cold gas or gasmixture that was pre-cooled using one or more different condensed gaseshaving a low boiling point.
 2. Method according to claim 1,characterized in that the fine-particle, powder-form solid substanceshave an average particle size of less than 5 μm, preferably less than 1μm.
 3. Method according to claim 1, characterized in that thefine-particle, powder-form solid substances to be cooled and filled areinorganic or organic pigments.
 4. Method according to claim 1,characterized in that the fine-particle, powder-form solid substances tobe cooled and filled are titanium dioxide, iron oxide, chromium oxide,photo-resistant pigments, colored pigments, metal pigments, magneticpigments, or carbon blacks.
 5. Method according to claim 1,characterized in that the fine-particle, powder-form solid substance tobe cooled and filled is cement.
 6. Method according to claim 1,characterized in that the fine-particle, powder-form solid substances tobe filled are temperature-sensitive compounds or solid substances coatedwith temperature-sensitive compounds.
 7. Method according to claim 1,characterized in that the fine-particle, powder-form solid substancesare ground before the process step of direct cooling.
 8. Methodaccording to claim 1, characterized in that the fine-particle,powder-form solid substances are pigments that are directly cooledbetween the process step of steam jet grinding and the process step offilling into bulk material packaging or mobile bulk material containers,by the addition of a cooling medium.
 9. Method according to claim 8,characterized in that of the mixture of ground pigment and gas phasethat contains steam, which is present immediately after the steam jetgrinding, part of the gas phase that contains steam is first removedfrom the ground pigments, using a dust separator and/or a dust filter,and subsequently the ground pigments are cooled by means of directcooling, using a cooling medium.
 10. Method according to claim 1,characterized in that the cooling medium used for direct coolingpreferably has a temperature of less than 0° C., preferably less than−20° C., particularly preferably less than −40° C.
 11. Method accordingto claim 1, characterized in that the fine-particle, powder-form solidsubstances are transported pneumatically for filling into bulk materialpackaging or mobile bulk material containers, and that the gas used forthe pneumatic transport is used as the cooling medium for directcooling, whereby this gas was cooled either indirectly in a heatexchanger, by means of condensed gases having a low boiling point, ordirectly, by injection of one or more different condensed gases having alow boiling point.
 12. Method according to claim 1, characterized inthat the cooling medium is metered into the transport line in thepneumatic transport of the fine-particle, powder-form solid substances.13. Method according to claim 1, characterized in that gaseous nitrogenor gaseous carbon dioxide is used as the cooling medium.
 14. Methodaccording to claim 1, characterized in that liquid nitrogen or liquid orsolid carbon dioxide is used as the cooling medium.
 15. Method accordingto claim 1, characterized in that the fine-particle, powder-form solidsubstances are cooled within the short period of time that is requiredfor mixing with the cooling medium, by at least 20° C., preferably by atleast 50° C.
 16. Method according to claim 1, characterized in that thefine-particle, powder-form solid substances are cooled to a maximum of100° C., preferably a maximum of 70° C.
 17. Method according to claim 1,characterized in that the cooling medium is introduced into thetransport gas for the pneumatic transport of the fine-particle,powder-form solid substances before the transport gas makes contact withthe solid substances.
 18. Method according to claim 1, characterized inthat the cooling medium used for direct cooling contains less than0.0001 parts by mass water, and that the dew point of the gas phase thatcontains solid substances is lowered in this manner.
 19. Methodaccording to claim 1, characterized in that the fine-particle,powder-form solid substances are filled into paper or plastic bags aftercooling has taken place.
 20. Method according to claim 1, characterizedin that the fine-particle, powder-form solid substances are filled intosilo vehicles after cooling has taken place.
 21. Fine-particle,powder-form solid substances produced according to claim 1, located inbulk material packaging, characterized in that the composition of thegas phase between the pigment particles contains less than 20 wt.-%oxygen, preferably less than 15 wt.-% oxygen.
 22. Fine-particle,powder-form solid substances produced according to claim 1, located inbulk material packaging, characterized in that the composition of thegas phase between the pigment particles contains a mass ratio ofnitrogen to oxygen of more than 4, preferably more than 5.7.
 23. Devicefor direct cooling of fine-particle, powder-form solid substancesaccording to claim 1, characterized in that this device consists of asupply container for condensed gases having a low boiling point, aninsulated connecting line between the supply container and the transportline for pneumatic transport of the fine-particle, powder-form solidsubstances, a nozzle for introduction of the condensed gases having alow boiling point into the transport line, and a control and regulationdevice.